Activation of nicotinic acetylcholine receptors augments calcium channel-mediated exocytosis in rat pheochromocytoma (PC12) cells.
The functional effect of activating Ca2+-permeable neuronal nicotinic acetylcholine receptors (nAChRs) on vesicle secretion was studied in PC12 cells. Single cells were patch-clamped in the whole-cell configuration and stimulated with either brief pulses of nicotine to activate the Ca2+-permeable nAChRs or with voltage steps to activate voltage-dependent Ca2+ channels. Membrane capacitance was used as a measure of vesicle secretion. Activation of nAChRs by nicotine application to cells voltage clamped at -80 mV evoked secretion. This secretion was completely abolished by nicotinic antagonists. When the cells were voltage clamped at +20 mV in the presence of Cd2+ to block voltage-activated Ca2+ channels, nicotine elicited a small amount of secretion. Most interestingly, when the nAChRs were activated coincidentally with voltage-dependent Ca2+ channels, secretion was augmented approximately twofold over the secretion elicited with voltage-dependent Ca2+ channels alone. Our data suggest that Ca2+ influx via nAChRs affects Ca2+-dependent cellular functions, including vesicle secretion. In addition to the secretion evoked by nAChR activation at hyperpolarized potentials, we demonstrate that even at depolarized potentials, nAChRs provide an important Ca2+ entry pathway underlying Ca2+-dependent cellular processes such as exocytosis.
Harkins
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AB
Department of Pharmacological and Physiological Sciences, The University of Chicago, Chicago, Illinois 60637, USA. amy@drugs.bsd.uchicago.edu
Fox
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AP
D000818:Animals; D001711:Biotransformation / Q000187:drug effects / Q000502:physiology; D002104:Cadmium / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D004558:Electric Stimulation; D004594:Electrophysiology; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D016716:PC12 Cells; D018408:Patch-Clamp Techniques; D051381:Rats; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000378:metabolism*
D015220:Calcium Channels; D011978:Receptors, Nicotinic; D002104:Cadmium